TNF-alpha-induced NF-kappaB signaling reverses age-related declines in VEGF induction and angiogenic activity in intervertebral disc tissues.

We previously demonstrated that VEGF and its receptors were expressed in human herniated discs (HD). TNF-alpha induced VEGF, resulting in neovascularization of disc tissues in a model of HD. The goal of the current research was to investigate the precise role of TNF-alpha-induced VEGF and the mechanism of angiogenesis in disc tissues. We performed ELISAs, Western blots, and immunohistological examinations to assess the role of TNF-alpha-induced VEGF using organ disc cultures with wild type, TNF receptor 1-null (TNF-RI(null)), or TNF receptor 2-null (TNF-RII(null)) mice. VEGF induction was inhibited when we used TNF-RI(null)-derived disc tissues. NF-kappaB pathway inhibitors also strongly suppressed VEGF induction. Thus, TNF-alpha induced VEGF expression in disc cells primarily through the NF-kappaB pathway. In addition, VEGF immunoreactivity was detected predominantly in annulus fibrosus cells and increased after TNF-alpha stimulation. TNF-alpha treatment also resulted in CD31 expression on endothelial cells and formation of an anastomosing network. In contrast, angiogenic activity was strongly inhibited in the presence of NF-kappaB inhibitors or anti-VEGF antibody. Our data show angiogenesis activity in disc tissues is regulated by VEGF and the NF-kappaB pathway, both of which are induced by TNF-alpha. The level of angiogenic activity in disc tissues was closely related to aging. Because neovascularization of HD is indispensable for HD resorption, the prognosis of HD and the rate of the resorption process in patients may vary as a function of the patient's age.